Fuel tank cap



FIG. 1 is a perspective view of a fuel tank cap showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a right side view thereof; and,

FIG. 7 is a left side view thereof.

In FIG. 3 the broken lines show interior element of a fuel tank cap and form no part of the claimed design. 

The ornamental design for a fuel tank cap, as shown and described. 